This invention relates to an improved solenoid apparatus for operating valves such as hydraulic/air valves or other mechanical devices.
In prior art solenoid apparatus of the type disclosed in U.S. Pat. No. 3,633,139 for mechanically actuating hydraulic/air valves and other mechanical devices, a shading coil is provided to suppress noise generated by the pulsatile attractive force associated with the armature and stationary core of the solenoid when single-phase AC current flows in the solenoid coil. The shading coil is usually brazed to one of the opposing faces of the stationary core and armature.
In such a case, the shading coil is liable to become detached due to shock caused when the armature collides with the stationary core, etc. and/or by vibration of the valve per se. Consequently there is a possibility the solenoid may break down. Besides, there are the disadvantages that the shading coil is expensive and requires a large number of man-hours for installation.
In addition, a solenoid which incorporates a shading coil for use with alternating current is sometimes unusable as a DC solenoid even though the coil assembly including the coil and yoke are replaced with a DC coil assembly including a coil and yoke, and the remaining portion of the solenoid sealed off with a pressure proof tube cannot be used with both alternating and direct currents.